1. Field of the Invention
The present invention generally relates to dynamic braking system excitation and control for diesel electric locomotives and, more particularly, to a power monitor which monitors the operation of the dynamic braking system for each locomotive of a consist.
2. Description of the Prior Art
Locomotive dynamic braking in diesel electric locomotives is used to retard locomotive speed through the conversion of kinetic energy to electrical energy. This is accomplished by connecting the traction motors as separately excited generators with field current being provided by the main generator. Electrical loading is provided by resistive grids which are connected to the traction motor armature circuits during dynamic braking, thus convening the electrical energy to heat energy radiated by the grids. The braking grids are cooled by a blower to prevent overheating. The grid current is determined by the speed of the locomotive and the amount of excitation current applied to the motor fields.
The dynamic braking system is protected in several ways. A dynamic braking regulator module senses a voltage across a portion of one braking grid, this voltage being proportional to the grid (and armature) current. The dynamic braking regulator module operates to limit the excitation current of the motor fields to a value that prevents armature and grid current from increasing above a maximum safe current. A dynamic brake grid protection system module operates in the event of a blower motor failure to disable the brake relay. A dynamic brake protection module contains a motor field protection circuit and a brake warning circuit. The motor field protection circuit operates to protect the motor fields in the event the field excitation current rises above a safe value, while the brake warning circuit provides backup protection for the brake grids by decreasing motor field excitation if grid current increases above a safe value. If a brake grid opens, an open circuit protection relay operates to disable the brake relay.
These various protective circuits prevent catastrophic destruction of the locomotive brake grid and traction motors in the case of a fault occurring during dynamic braking. The engineer is informed of a fault in the dynamic braking system by suitable instrumentation display so that appropriate action can be taken. A problem arises, however, in a typical railroad consist comprising multiple locomotives and cars. The number of locomotives for a given consist is determined on the basis of both the traction power and the dynamic braking required taking into consideration weight and terrain. The several locomotives are interconnected by means of a MU (multiple unit) cable, and the engineer in the cab of the lead locomotive has control over all locomotives in the consist. However, the engineer does not have an instrumentation display to indicate the traction power and dynamic brake system operation of each locomotive in the consist. As a result, a fault may occur in one of the locomotives, and the engineer would be unaware of the fault. For example, if a brake grid circuit in the dynamic braking system of one of the locomotives were open, the amount of dynamic braking that would be available would be less than that which the locomotive engineer thinks that the consist has.